1. Field of the Invention
The present invention relates to a proximity sensor, and more particularly, to a proximity sensor using a photosensor reduced in power consumption compared with a conventional one.
2. Description of the Related Art
A conventional proximity sensor using a photosensor is capable of detecting a finger or the like coming close thereto by emitting light by itself and detecting reflection light on the finger or the like coming close thereto by means of the photosensor (see, for example, Japanese Patent Application Laid-open No. 2004-56905 (FIG. 1)).
FIG. 10 illustrates a circuit block diagram of a non-contact switch using the conventional proximity sensor. The non-contact switch 10 includes a proximity sensor 29 of type using reflection light having a light receiving part 27 and a light projecting part 28, a switch circuit 31 connected in series to a load such as a lighting tool 30 as an example of an electronic device, a triac (example of switch means) 32 constituting a semiconductor switch element of the switch circuit 31, a switch control section 33 for turning ON/OFF the triac 32 based on an output of the proximity sensor 29, and a power supply section 34 for supplying power to those components.
The proximity sensor 29 has a well-known configuration, in which the light projecting part 28 using a light-emitting diode emits an infrared pulse to be reflected on a human hand 35 as an example of a target, and when the light receiving part 27 using a phototransistor or a photodiode receives light reflected off the human hand 35, the proximity sensor 29 sends an output of ON to the switch control section 33.
When a signal is input to a gate of the triac 32 provided in the switch circuit 31, the triac 32 becomes a conductive element with respect to AC power supply after the input of the signal until the polarity of AC power supply is changed. If the proximity sensor 29 is turned ON, the triac 32 is turned ON based on a signal transmitted from the switch control section 33.
When the proximity sensor 29 detects the human hand 35 or the like, if the human hand 35 moves back and forth in front of the proximity sensor 29, the proximity sensor 29 is turned ON/OFF for each detection of the human hand 35. This may result in unnaturally high responsivity of the proximity sensor 29. As a countermeasure, for example, the switch control section 33 is provided with a timer circuit for about 1 to 2 seconds so as to realize a delay circuit for preventing the triac 32 from being turned OFF unless the timer circuit counts up immediately after the proximity sensor 29 is turned ON.
The switch control section 33 is further provided with an operation indicator 23 which lights up when the proximity sensor 29 is turned ON. The operation indicator 23 lights up only when the proximity sensor 29 is turned ON and the triac 32 is turned ON. Alternatively, the operation indicator 23 may employ a two-color light-emitting diode so that green (or yellow) light may be emitted when the proximity sensor 29 is OFF while red light may be emitted when the proximity sensor 29 is ON. Note that, the triac 32 may be connected to a neon tube at both ends thereof for display during OFF of the triac 32.
With such a configuration of the non-contact switch 10 of the conventional technology, under a state in which no power is supplied to the lighting tool 30, that is, when the triac 32 of the non-contact switch 10 is in a non-conductive state, the power supply voltage is applied across the triac 32, and accordingly the power supply section 34 rectifies the power supply voltage to a constant voltage to be supplied to the switch circuit 31, the proximity sensor 29, and the switch control section 33. Then, when the proximity sensor 29 detects the human hand 35 and thereby starts to operate, the proximity sensor 29 supplies an output of the detection to the switch control section 33 so that a signal may be sent to the switch circuit 31, specifically, a signal may be sent to the triac 32 with a phase angle of 15° to 20° with respect to the half wavelength) (180°, to thereby turn ON the switch circuit 31.
Across the triac 32, a small voltage as a part of the power supply voltage is generated. The power supply section 34 rectifies the generated voltage to obtain minute power, and converts the power to a constant DC voltage to be supplied to the switch circuit 31, the proximity sensor 29, and the switch control section 33. This configuration enables power supply even if the switch circuit 31 continues to be turned ON.
The conventional proximity sensor using a photosensor employs a proximity sensor of type using reflection light and needs to emit light by itself, which leads to a problem of very large current consumption, and further the light receiving part for detecting the reflection light has a complicated circuit configuration, which leads to a problem of large current consumption. In addition, there is another problem that the battery life for battery drive significantly reduces, which makes it difficult to utilize battery drive.